Numerous drugs are known for their unpleasant taste and the prior art has disclosed products to mask these drugs from unpleasant tastes. To be effective coatings must not merely mask the taste by overcoming the unpleasant taste but also delay the hydration of the drug until it passes the mouth and taste buds.
U.S. Pat. No. 4,797,288 discloses a drug delivery system which may be chewed or swallowed that contains a hydrophobic matrix of an emulsifier, an edible material having a melting point below 100.degree. C. selected from a fatty acid, natural waxes, synthetic waxes and mixtures thereof. The matrix is coated with a coating consisting of fatty acids and wax combination. The coat level is 200% to 400% by weight resulting in a low drug potency. Due to the high coating levels employed and materials employed in the matrix it is expected that the drug delivery rate is retarded.
European Patent 455 391 discloses granules of polyglycerol esters and a pharmaceutically active material made in a fluidized bed. The fluidized bed is heated and the material is entrained in the heated fluidized bed until the polyglycerol esters are melted and the particles are agglomerated.
U.S. Pat. No. 5,399,357 discloses a stable controlled release pharmaceutically acceptable matrix preparation consisting of a fatty acid ester of polyglycerol and microcrystalline waxes. The drug dissolution rate is retarded resulting in prolonged release not suitable for immediate drug action in the body. The system claimed is a matrix not a coating.
Although these prior disclosures provide taste masked compounds, the described systems do not provide a dissolution rate that is suitable for a pharmaceutical product where the drug is immediately released and available for drug absorption. Those with skill in the art will appreciate that the therapeutic effect will thus be delayed, see for example, "Dissolution, Bioavailability and Bioequivalence" by H. M. Abdou, Mack Publishing Company, 1989.
Additionally, the above identified disclosures do not provide any data to show that the systems are physically stable. If the systems are not stable, the delivery of the active pharmaceutical ingredient can vary over time based on environmental conditions and the length of time the pharmaceuticals have been in storage.
Therefore alternative formulations which provide uniform, stable dissolution rates during storage in various environmental conditions but which also provide rapid dissolution once ingested is highly desirable.